As the Earth and Venus circle around the sun in their respective
orbits, their changing geometry causes Venus brightness to vary.
As you might expect, it generally tends to be brighter when it is
closer to Earth. However, this isnt always true because Venus is
an "inferior" planet.

Astronomers use "inferior" to mean "closer to the sun" rather
than "lower in quality." So, the planets Mercury and Venus are
both known as "inferior planets."

As a result of its orbit being closer to the sun than the
Earth's, Venus passes between the Earth and the sun once every
584 days. This is known as " inferior
conjunction," and last occurred on Oct. 29.

Even though Venus was closest to Earth on that date, it was for
all intents and purposes invisible. That's because on Oct. 29
Venus was almost entirely backlit, except for a tiny amount of
sunlight leaking through its upper atmosphere.

But over the last five weeks, Venus has moved along its orbit
such that, while it is farther from the Earth than it was in late
October, it is now more brightly illuminated by the sun from the
side. This makes more of
Venus' cloud tops visible and gives the planet a brilliant
shine.

On Dec. 4, these two factors balance out to result in Venus being
the brightest it can be. Astronomers measure brightness using a
term called magnitude. The lower the number of an object's
magnitude, the brighter it is in the sky.

This Saturday, Venus will have a magnitude of minus 4.9, while
the sun is minus 26.8, the moon is minus 12.7, and the brightest
star Sirius is minus 1.4.

When Venus is this bright, it is easily seen in a clear blue sky
with the naked eye, if you know precisely where to look. The best
way to find it is on the day when it is closest to the moon,
since its much easier to find the bigger brighter moon in a blue
sky.

A good example was yesterday morning Thursday, Dec. 2
around 9:30 a.m. ET, when both the Moon and Venus will be
due south (for observers in the northern hemisphere) and Venus
will be 7 degrees (1 binocular field) above the moon.

You can find Venus first with binoculars, and then try to spot it
with your naked eye. If you miss it this time, you can try again
on Dec. 31.

In binoculars or a small telescope, Venus now appears as a narrow
crescent, similar to the moon. In fact, if you checked the
pre-dawn sky on Thursday morning, you may have seen the
26-day-old moon right next to Venus, while both showed almost the
same phase illumination, since both were being lit by the sun
from about the same angle.